Facilitating exercise using external stimulation, including by sending electrical pulses to contract or otherwise activate the targeted or involved muscles, is known in the art. Typically, the electrical pulses applied are generated by an external stimulator, and travel through associated wires to electrode pairs placed on the skin adjacent the muscle(s) to be contracted. The electricity passing through the skin causes the targeted muscle fibers to activate or contract, even without voluntary control by the subject. Accordingly, such stimulation is frequently used in situations where the subject is incapacitated or otherwise unable to control function of the muscles, such as where an injury to the brain or associated portion of the nervous system has occurred.
Despite the widespread past use of electrical stimulation for exercising muscles, certain limitations in the application of this technology and the results produced remain. For instance, while electrically stimulating resting leg muscles alone provides a moderate benefit, a significantly better degree of exercise may be achieved when the legs are also subjected to movement through a particular range of motion (ROM). Although such movements could be manually done by a physical therapist or like assistant concurrently with the application of electrical stimulation, the benefit would be greater if the leg muscles being stimulated, as well as others that are not, undergo active or dynamic loading (and especially the type of loading that would occur as the result of normal exercise or ambulation). Such dynamic loading is thought to help the otherwise paralyzed or inactive muscles build mass, strength, and endurance at levels that cannot be achieved through stimulation alone, and also reduces the rate of loss in bone mineral density.
Many incapacitated subjects, and in particular those who have experienced spinal cord injury resulting in the partial or total loss of use of the lower extremities, often find exercise via mere electrical stimulation through contact electrodes tedious. The stimulation of otherwise non-operational or paralyzed muscles typically occurs while the subject simply lies prostrate or sits because of the inability to stand or ambulate independently. Besides again avoiding the desirable dynamic loading, the bored subject undergoing treatment while laying still on a table also does not gain the mental and emotional benefits resulting from the exercise and the concomitant sense of accomplishment. Consequently, “exercising” via stimulation alone can be viewed negatively by those most in need of the resultant benefits, and does not provide the desired level of encouragement to promote the most expeditious recovery, where possible.
Even if current stimulation techniques are applied to closed-chain leg exercises under partial bodyweight loading, the inability to account for differences in the ground reactive force, or GRF, experienced by each leg creates potential problems. If the muscles of one leg are doing more of the work than those of the other, and this disparity not kept in check, less-than-optimal results may be achieved. This is particularly true when the loss of leg muscle function is asymmetrical.
Accordingly, a need is identified for a manner in which to combine the benefits achieved through electrical muscle stimulation with those of load bearing, closed-chain exercise, including for subjects with a full or limited inability to use the muscles their lower extremities (and, in particular, one or both of their legs). This may even include situations where a full loss of muscle control has occurred, such as in the case of paraplegia, or control is lost to different degrees in each leg, such as in the case of stroke.